Image display apparatus and X-ray computed tomography apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing of a computed tomography (CT) image generated by using multi-arrayed detecting elements along a body axis, and especially to an image display apparatus and an X-ray CT apparatus for an image reconstruction processing using algorithm capable of reproducing a cone angle in the body axis direction faithfully and for clarifying a range that the image reconstruction processing is possible.

2. Description of the Related Art

In a generally employed X-ray CT apparatus, an X-ray tube and an X-ray detector with a plurality of segments (a plurality of arrayed detecting elements along a body axis direction (channel direction)) are oppositely placed to interpose an object, for example, a patient. The X-ray tube irradiates an X-ray beam to a predetermined site of the patient while rotating around the patient at “360°” together with the X-ray detector. The X-ray detector measures an X-ray dose that transmits the predetermined site of the patient as projection data. By the image reconstruction processing based on the projection data by using a computer, a CT image of the predetermined site is obtained.

There is a generally employed X-ray CT apparatus that has the X-ray detector with the segments from “2” to “64” on the body axis direction, known as “multi”, now in the world. About the generally employed X-ray CT apparatus, there is the following characteristic. When an art used in the generally employed multi-X-ray CT apparatus is just applied to an X-ray CT apparatus having an X-ray detector with “64” or more segments, there is a following problem.

It depends on a length of the segments along the body axis direction, a distance between the X-ray tube and the object, a field of view (FOV), and a cone angle, but in a case where the X-ray detector with “64” or more segments on the body axis direction is used, two areas are expected to appear on the CT image, that is, a deteriorating area caused by the relatively insufficient projection data due to the cone angle of the X-ray, and a non-deteriorating area with relatively sufficient projection data. However, when only the non-deteriorating area tends to appear on the CT image by using the generally employed multi-X-ray CT having the X-ray detector with the segments from “2” to “64”, the deteriorating area appeared on the CT image was rarely distinguished on displaying.

In a case where the deteriorating area on the CT image is intended to be masked, an operator is unable to identify a range to be masked upon CT inspection, and accordingly, fails to determine whether or not the required scan area covers the predetermined site of the patient before a scan.

SUMMARY OF THE INVENTION

The present invention has taken into consideration the above-described problems, and it is an object of the present invention to provide the image display apparatus and the X-ray CT apparatus, an image that can effectively perform an inspection and an interpretation of radiogram is offered.

To solve the above-described problems, the present invention provides the image display apparatus that acquires projection data while rotating an X-ray source for emitting an X-ray beam and an X-ray detector including multi-arrayed detecting elements along a slice direction around a rotary axis, and displays a CT image that is reconstructed by performing a back projection in consideration with a cone angle of the X-ray beam, comprising: an area arithmetic unit configured to obtain information with respect to a position of a deteriorating area appeared around an end on an acquisition range of the projection data under an influence of the cone angle; and a display controlling processing unit configured to control a displaying of the CT image in a display format that be discriminable the deteriorating area from an area other than the deteriorating area, based on the information with respect to the position of the deteriorating area.

To solve the above-described problems, the present invention provides the X-ray computed tomography apparatus that acquires projection data while rotating an X-ray source for emitting an X-ray beam and an X-ray detector including multi-arrayed detecting elements along a slice direction around a rotary axis, and reconstructs a CT image by performing a back projection in consideration with a cone angle of the X-ray beam, comprising: an area arithmetic unit configured to obtain information with respect to a position of a deteriorating area appeared around an end on an acquisition range of the projection data under an influence of the cone angle; and an image processing unit configured to perform an image processing for the CT image to be discriminable the deteriorating area from an area other than the deteriorating area.

To solve the above-described problems, the present invention provides the X-ray computed tomography apparatus that acquires projection data while rotating an X-ray source for emitting an X-ray beam and an X-ray detector including multi-arrayed detecting elements along a slice direction around a rotary axis, and reconstructs a CT image by performing a back projection in consideration with a cone angle of the X-ray beam, comprising: a display device configured to display an image for a positioning of an object that is obtained by a scan for the object and an image of a mark indicating a scan range by superimposing, and to display the image of the mark on the image for the positioning so as to be discriminable the deteriorating area; and an input device configured to enable a signal input of the scan range to obtain the CT image.

To solve the above-described problems, the present invention provides the X-ray computed tomography apparatus that acquires projection data while rotating an X-ray source for emitting an X-ray beam and an X-ray detector including multi-arrayed detecting elements along a slice direction around a rotary axis, and reconstructs a CT image by performing a back projection in consideration with a cone angle of the X-ray beam, comprising: an image processing unit configured to perform at least any one of operations to hide a display, to change a color, and to lower a contrast with respect to the deteriorating area on a scanogram for a positioning of an object that is obtained by a scan for the object; a display device configured to display the scanogram generated by the image processing unit, and an image of a mark indicating a scan range by superimposing; and an input device configured to enable a signal input of the scan range to obtain the CT image.

To solve the above-described problems, the present invention provides the X-ray computed tomography apparatus that acquires projection data while rotating an X-ray source for emitting an X-ray beam and an X-ray detector including multi-arrayed detecting elements along a slice direction around a rotary axis, and reconstructs a CT image by performing a back projection in consideration with a cone angle of the X-ray beam, comprising: an area arithmetic unit configured to obtain information with respect to a position of a deteriorating area appeared around an end on an acquisition range of the projection data under an influence of the cone angle; and an image processing unit configured to perform an image processing for the CT image so as to be discriminable the deteriorating area.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

<figref idrefs="DRAWINGS">FIG. 1</figref> is a block diagram of an embodiment of an X-ray CT apparatus according to the present invention;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a functional block diagram of an operation console in the embodiment of the X-ray CT apparatus;

<figref idrefs="DRAWINGS">FIG. 3</figref> is a diagram of a planar sagittal showing an imaging space at a predetermined site of a patient;

<figref idrefs="DRAWINGS">FIG. 4</figref> is a diagram to explain how an “M_FOV” is generated;

<figref idrefs="DRAWINGS">FIG. 5</figref> is a diagram of an example showing a map of area outside imaging space and a map of deteriorating area on a planar CT;

<figref idrefs="DRAWINGS">FIG. 6</figref> is a pattern diagram showing an example of display method of an image including a CT image;

<figref idrefs="DRAWINGS">FIG. 7</figref> is a pattern diagram showing an example of display method of the image including the CT image;

<figref idrefs="DRAWINGS">FIG. 8</figref> is a pattern diagram showing an example of display method of the image including the CT image;

<figref idrefs="DRAWINGS">FIG. 9</figref> is a diagram showing an example of the map of area outside imaging space and the map of deteriorating area;

<figref idrefs="DRAWINGS">FIG. 10</figref> is a diagram showing an example of display method of the image including an MPR (sagittal) image;

<figref idrefs="DRAWINGS">FIG. 11</figref> is a diagram showing an example of display method of the image including the MPR image;

<figref idrefs="DRAWINGS">FIG. 12</figref> is a conceptual diagram showing an example of display method of a scanogram;

<figref idrefs="DRAWINGS">FIG. 13</figref> is a block diagram showing an embodiment of a image display apparatus according to the present invention; and

<figref idrefs="DRAWINGS">FIG. 14</figref> is a functional block diagram showing the embodiment of the image display apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of an image display apparatus and an X-ray CT apparatus according to the present invention will be described referring to the accompanied drawings.

There are various types of the X-ray CT apparatus, for example, a type of “ROTATE/ROTATE” in which an X-ray tube and an X-ray detector are integrally rotated around an object, a type of “STATIONARY/ROTATE” in which a large number of detecting elements are ring-like arrayed such that only the X-ray tube is rotated around the object, and the like. The present embodiment is applicable to the X-ray CT apparatus of arbitrary type. In the embodiment, the explanation with respect to the X-ray CT apparatus of the type of “ROTATE/ROTATE” which has been used as the mainstream trend will be made hereinafter. In order to reconstruct a single slice of CT image data, projection data of full circle of the object at approximately “360°” are required. Alternatively, the projection data of half circle of the object at “180°” plus a view angle are required in case of a half scan method. The present embodiment is applicable to any one of the aforementioned reconstruction methods. As a mechanism for converting an incident X-ray into an electric charge, a type of indirect conversion and a type of direct conversion have been employed as the mainstream trend. In the type of indirect conversion, the incident X-ray is converted into a light by a fluorescent material such as a scintillator, and the light is converted into the electric charge using a photoelectric conversion element such as a photodiode. Meanwhile, the type of direct conversion of the incident X-ray is performed by forming an electron-hole pair within a semiconductor so as to be conducted to an electrode, that is, using a photoconductive effect of the X-ray. An arbitrary type of the aforementioned X-ray detector element may be employed. Recently, an X-ray CT apparatus with so-called multi-X-ray tube has been increasingly produced and the peripheral techniques have also been developed. In the X-ray CT apparatus with so-called multi-X-ray tube, plural pairs of the X-ray tube and the X-ray detector are installed in a rotary frame. The present embodiment is applicable to either the generally employed the X-ray CT apparatus with the single tube or the X-ray CT apparatus with so-called multi-X-ray tube. In the embodiment, the X-ray CT apparatus with the single tube will be described hereinafter.

<figref idrefs="DRAWINGS">FIG. 1</figref> is a block diagram of an embodiment of an X-ray CT apparatus according to the present invention.

<figref idrefs="DRAWINGS">FIG. 1</figref> shows an X-ray CT apparatus <b>10</b> which acquires projection data while rotating the X-ray source that irradiates an X-ray beam and the X-ray detector including a plurality of arrayed detecting elements along a z-axis direction (body axis direction, slice direction) around a rotary axis, and reconstructs the CT image at each slice by performing a back projection in consideration with an cone angle of the X-ray beam. The X-ray CT apparatus <b>10</b> has a gantry <b>11</b> on which an object M (patient M<b>1</b> or cylinder M<b>2</b>) is executed a scan with the X-ray, a table <b>12</b> that conveys the object M through the cavity of the gantry <b>11</b> in the z-axis direction, and an operation console <b>13</b> which controls the operation of the gantry <b>11</b> and reconstructs the CT image (axial image) based on the data transmitted from the gantry <b>11</b> so as to be output (displayed).

The gantry <b>11</b> operable in a tilt direction (not shown) has a rotary unit <b>15</b> and a fixed unit (not shown). The rotary unit <b>15</b> of the gantry <b>11</b> has an X-ray tube <b>21</b>, a collimator <b>22</b>, an opening control motor <b>23</b>, an X-ray detector <b>24</b>, and a data acquisition system (DAS) <b>25</b>. The X-ray tube <b>21</b> and the collimator <b>22</b> are placed opposite the X-ray detector <b>24</b> such that the cavity of the gantry <b>11</b>, that is, the object M is interposed therebetween. The rotary unit <b>15</b> is structured to rotate around the cavity while keeping the aforementioned positional relationship.

The fixed unit has a main controller <b>31</b>, interfaces (IFs) <b>32</b><i>a </i>and <b>32</b><i>b</i>, an X-ray tube controller <b>33</b>, an opening control motor driver <b>34</b>, a rotary motor <b>35</b>, a rotary motor driver <b>36</b>, a table motor <b>37</b> and a table motor driver <b>38</b>.

The driving operation of the X-ray tube <b>21</b> as the X-ray source is controlled by the X-ray tube controller <b>33</b> such that the X-ray is irradiated from a tube (not shown) of the X-ray tube <b>21</b> to the X-ray detector <b>24</b>.

The driving operation of the collimator <b>22</b>, having an opening for controlling the irradiation range of the X-ray from the X-ray tube <b>21</b>, is controlled by the opening control motor driver <b>34</b>.

The X-ray detector <b>24</b> has a plurality of segments (a plurality of the arrayed X-ray detecting elements along the z-axis direction (channel direction)) that detect the X-ray irradiated from the X-ray tube <b>21</b> via the collimator <b>22</b> and the cavity. In the z-axis direction of the X-ray detector <b>24</b>, “64” or more segments of the X-ray detecting elements, for example, “256” segments are arranged in parallel with one another.

The data acquisition system <b>25</b> acquires signals output from the respective detection channels of the X-ray detector <b>24</b> as the projection data.

The main controller <b>31</b> analyzes respective commands received from the operation console <b>13</b> via the IF <b>32</b><i>a</i>, based on which various control signals are output to the X-ray tube controller <b>33</b>, the opening control motor driver <b>34</b>, the rotary motor driver <b>36</b>, the table motor driver <b>38</b> and the data acquisition system <b>25</b>, respectively.

The X-ray tube controller <b>33</b> transmits a drive signal to the X-ray tube <b>21</b> so as to generate the X-ray.

The opening control motor driver <b>34</b> transmits a drive signal to the opening control motor <b>23</b> so as to adjust the aperture of the collimator <b>22</b>.

The rotary motor driver <b>36</b> transmits a drive signal to the rotary motor <b>35</b> so as to rotate the rotary unit <b>15</b> around the cavity while keeping its positional relationship.

The table motor driver <b>38</b> transmits a drive signal to the table motor <b>37</b> so as to convey the table <b>12</b> in the z-axis direction.

The projection data acquired by the data acquisition system <b>25</b> are transmitted to the operation console <b>13</b> via the IF <b>32</b><i>b. </i>

The operation console <b>13</b> is structured based on a computer as so-called workstation and may be bilaterally communicated with the network N, for example, local area network (LAN) constructed in the hospital. The operation console <b>13</b> is mainly formed of a basic hardware including a central processing unit (CPU) <b>41</b>, a memory <b>42</b>, a hard disc (HD) <b>44</b>, IFs <b>45</b><i>a</i>, <b>45</b><i>b </i>and <b>45</b><i>c</i>, an input device <b>46</b> and a display device <b>47</b>. The CPU <b>41</b> is interconnected with the respective units of the hardware that forms the operation console <b>13</b> via a bus B<b>1</b> as the common signal transmission path. A drive for medium <b>48</b> may be added to the operation console <b>13</b>.

The CPU <b>41</b> executes a program stored in the memory <b>42</b> in response to an instruction input through the operation of the input device <b>46</b> by an operator. Alternatively, the CPU <b>41</b> executes the program stored in the HD <b>44</b>, the program transferred from the network N to the IF <b>45</b><i>c </i>to be installed in the HD <b>44</b>, or the program read from the recording medium set in the drive for medium <b>48</b> through loading to the memory <b>42</b>.

The memory <b>42</b> serves as a read only memory (ROA) and a random access memory (RAM) to store an initial program loading (IPL), a basic input/output system (BIOS) and the data as a storage device. The memory <b>42</b> may be a work memory of the CPU <b>41</b>, and temporarily store the data.

The HD <b>44</b> is formed of a non-volatile semiconductor disk serving as the storage device, and stores the program installed in the operation console <b>13</b> (including operating system (OS) in addition to an application program) and the data. The OS may be structured to supply a graphical user interface (GUI) that allows the input device <b>46</b> to perform the basic operation for a graphics-laden display of the information for an operator.

The IFs <b>45</b><i>a</i>, <b>45</b><i>b </i>and <b>45</b><i>c </i>control the communication in accordance with the respective standards. The IFs <b>45</b><i>a </i>and <b>45</b><i>b </i>for communicating with the gantry <b>11</b> are connected to the IFs <b>32</b><i>a </i>and <b>32</b><i>b </i>of the gantry <b>11</b>, respectively. The IF <b>45</b><i>c </i>has a function to connectable to the network N via a telephone line and so on. Accordingly, the operation consol <b>13</b> is connected from the IF <b>45</b><i>c </i>to the network N.

A keyboard and a mouse operable by the operator may be employed as the input device <b>46</b> such that a signal input in accordance with an operation is transmitted to the CPU <b>41</b>. The operator is allowed to input a width of X-ray irradiated area (described later) in the z-axis direction to the operation console <b>13</b> via the input device <b>46</b>. The operator is allowed to set a scan range (described later) for obtaining the CT image by the input operation via the input device <b>46</b>.

A monitor may be employed as the display device <b>47</b>. The CT image may be displayed on the display device <b>47</b> by developing the image data in a memory, for example, a video random access memory (VRAM) (not shown) that develops the image data intended to be displayed.

The drive for medium <b>48</b> allows the medium to be detachably set such that the data (including the program) stored in the medium are read to be output onto the bus B<b>1</b>. The data supplied through the bus B<b>1</b> are written in the medium. The aforementioned medium may be supplied as a so-called package software.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a functional block diagram of the operation console <b>13</b>.

The operation console <b>13</b> (shown in <figref idrefs="DRAWINGS">FIG. 1</figref>) serves as an area arithmetic unit <b>55</b>, a CT scan executing unit <b>56</b>, a storage of projection data controlling unit <b>57</b> and an image processing unit <b>58</b> upon execution of the program by the CPU <b>41</b> of the operation console <b>13</b>. The respective units from <b>55</b> to <b>58</b> are structured to be operated by executing the program. However, they are not limited to the structure as described above. Whole or part of the respective units from <b>55</b> to <b>58</b> may be formed as the hardware provided in the operation console <b>13</b>.

The area arithmetic unit <b>55</b> has a function to obtain information with respect to a position of a deteriorating area (low quality area in the image data) generated around the end on an acquisition range of the projection data caused by the relative insufficiency of the projection data under an influence of the cone angle, a noise, and an image distortion based on a planar slice. More specifically, the area arithmetic unit <b>55</b> obtains the information with respect to an area outside an diameter of an imaging space, the position of the deteriorating area which appears around an end of the projection data acquisition range under the influence of the cone angle, and a position of a non-deteriorating area (normal quality area in the image data) other than the deteriorating area with relatively sufficient projection data, respectively based on the position information in the slice direction. The area arithmetic unit <b>55</b> has a non-deteriorating area generating unit <b>61</b>, a map of area outside imaging space generating unit <b>62</b>, and a map of deteriorating area generating unit <b>63</b>.

In the present embodiment, when the X-ray irradiation at each projection angle (view angle) is executed for an area formed by the imaging space and a distance (VDS, described later) of the z-axis direction, there is a case that there are both with projection data obtained at a certain projection angle and projection data obtained at an opposed projection angle (around “180” degrees) of the certain projection angle. In this case, a data area of the projection data obtained at the certain projection angle and a data area of the projection data obtained at the opposed projection angle are compared. And, an area that reconstructed a data area where the data area of the projection data obtained at the certain projection angle and the data area of the projection data obtained at the opposed projection angle are not crossover is defined as the “deteriorating area”.

The non-deteriorating area generating unit <b>61</b> has a function to generate the non-deteriorating area, appeared on the image data at each planar slice to assume a center of the rotary axis of the rotary unit <b>15</b> a center, based on the diameter of the imaging space, the width of the X-ray detector <b>24</b> in the z-axis direction, a distance between the x-ray tube <b>21</b> and the X-ray detector <b>24</b>, and a diameter of the non-deteriorating area on the planar slice at a distal end.

<figref idrefs="DRAWINGS">FIG. 3</figref> is a diagram of a planar sagittal showing the imaging space at a predetermined site of the patient M<b>1</b>.

An x-axis direction of the imaging space (shown in <figref idrefs="DRAWINGS">FIG. 3</figref>) is determined by the number of the cylindrical models containing reference material, for example, a water phantom, and the arrangement thereof, and represents the diameter (Calibration_Field_Of_View: Calib_FOV) of the cylindrical imaging space at the axial center in the z-axis direction. Meanwhile, the z-axis direction represents a width (Detector_Size: DS) of the X-ray irradiated area in the z-axis direction of the X-ray detector <b>24</b>, or a range (reconstruction_FOV) of the planar slice that can be reconstructed. As the “Calib_FOV” is determined by a diameter of a cylinder having the z-axis as an axial center, it may be kept constant by changing the z-axis direction.

The non-deteriorating area generating unit <b>61</b> has a function to generate a size (diameter) (Mask_FOV: M_FOV) of the deteriorating area to occur on each planar slice in the “reconstruction_FOV” at the rotary axis of the rotary unit <b>15</b> as the center, based on the “Calib_FOV”, the “DS”, the distance (focus center distance: FCD) between the X-ray tube <b>21</b> and the X-ray detector <b>24</b>, and a size (diameter) of the non-deteriorating area on the planar slice (distal end of the reconstruction_FOV) at the distal end in the z-axis direction of the X-ray detector <b>24</b> at the rotary axis of the rotary unit <b>15</b> as the center, that is, a “Minimum_Mask_FOV (MM_FOV)”. Farther, the “MM_FOV” may be input by the operator through the input device <b>46</b>, or preliminarily set. In addition, the “MM_FOV” preliminarily set by the independent operator or the inspection site may be used.

<figref idrefs="DRAWINGS">FIG. 4</figref> is a diagram to explain how the “M_FOV” is generated. <figref idrefs="DRAWINGS">FIG. 4</figref> only shows the plane of a first quadrant of the x-z coordinate system (planar sagittal system) with a gravity center of the imaging space as the base point. In <figref idrefs="DRAWINGS">FIG. 4</figref>, the “Calib_FOV” is expressed as a radius, that is, a “½_Calib_FOV”, the “DS” is expressed as a “½_DS”, the “MM_FOV” is expressed as a radius, that is, a “½_MM_FOV”. Referring to <figref idrefs="DRAWINGS">FIG. 4</figref>, the portion on the planar sagittal appeared as the non-deteriorating area on each planar slice at the rotary axis of the rotary unit <b>15</b> as the center is hatched.

For example, the operator inputs the “MM_FOV” into the operation console <b>13</b> through the input device <b>46</b> (shown in <figref idrefs="DRAWINGS">FIG. 1</figref>) so as to calculate the virtual width (Virtual_Detector_Size: VDS) of the X-ray detector <b>24</b> in the z-axis direction using the “MM_FOV”, the “FCD”, and the “DS” with a following Equation (1). In addition, according to <figref idrefs="DRAWINGS">FIG. 4</figref>, the “VDS” is expressed with a “½_VDS”.

<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>VDS</mi><mo>=</mo><mfrac><mrow><mn>2</mn><mo>×</mo><mi>FCD</mi><mo>×</mo><mi>DS</mi></mrow><mrow><mi>FCD</mi><mo>-</mo><mi>MM_FOV</mi></mrow></mfrac></mrow></mtd><mtd><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

In addition, a coordinate (Dist) of the z-axis direction at a predefined planar slice is operated based on a size (SegSize) of the detecting elements of the X-ray detector <b>15</b>, and a absolute value of a difference a segment number (Cseg) of the detecting element had at a center of the z-axis direction of the X-ray detector <b>24</b> and detecting element number (seg) at the predefined planar slice by a following Equation (2). <br />Dist=<i>abs</i>(<i>C</i>seg−seg)×SegSize  (2)

Therefore, a provisional “M_FOV” (tmpM_FOV) at the predefined planar slice is obtained by a following Equation (3). That is to say, the “tmpM_FOV” changes at each planar slice.

<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mtable><mtr><mtd><mrow><mi>tmpM_FOV</mi><mo>=</mo><mrow><mrow><mo>(</mo><mrow><mn>1</mn><mo>-</mo><mfrac><mi>Dist</mi><mi>VDS</mi></mfrac></mrow><mo>)</mo></mrow><mo>×</mo><mn>2</mn><mo>×</mo><mi>FCD</mi></mrow></mrow></mtd><mtd><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mtd></mtr></mtable></math></maths>

In addition, at the each planar slice, a small one is obtained as the “M_FOV”, based on the “Calib_FOV” and the “tmpM_FOV” by a following Equation (4). <br /><i>M</i>_FOV=min(<i>tmpM</i>_FOV,Calib_FOV)  (4)

For example, in a case of a planar slice S<b>1</b> during <figref idrefs="DRAWINGS">FIG. 4</figref>, the “M_FOV” seems to become a following Equation (5). <br /><i>M</i>_FOV=Calib_FOV  (5)

At the same time, in a case of a planar slice S<b>2</b> during <figref idrefs="DRAWINGS">FIG. 4</figref>, the “M_FOV” seems to become a following Equation (6). <br /><i>M</i>_FOV=tmpM_FOV  (6)

The map of area outside imaging space generating unit <b>62</b> (shown in <figref idrefs="DRAWINGS">FIG. 2</figref>) has a function to generate a map of area outside imaging space which is an area outside the imaging space on each planar slice around a reconstruction center, using a generally employed process based on the “Calib_FOV” and the “reconstruction_FOV”.

The map of deteriorating area generating unit <b>63</b> has a function to generate a map of deteriorating area of the deteriorating area appeared on each planar slice around a reconstruction center, based on the “Calib_FOV”, the “reconstruction_FOV”, and the “M_FOV” generated by the non-deteriorating area generating unit <b>61</b>. The diameter (rate) of the deteriorating area may vary depending on the planar slice within the “reconstruction_FOV” as shown in <figref idrefs="DRAWINGS">FIG. 4</figref>.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a diagram of an example showing the map of area outside imaging space and the map of deteriorating area on the planar CT (planar axial).

<figref idrefs="DRAWINGS">FIG. 5</figref> is a diagram of the planar slice S<b>2</b> (shown in <figref idrefs="DRAWINGS">FIG. 4</figref>), and shows the map T<b>1</b> of area outside imaging space and the map T<b>2</b> of deteriorating area in the case where the rotary axis of the rotary unit <b>15</b> (shown in <figref idrefs="DRAWINGS">FIG. 1</figref>) coincides with the reconstruction center. The map T<b>2</b> of deteriorating area is a doughnut-like map defined by a circular inner rim (dashed line in <figref idrefs="DRAWINGS">FIG. 5</figref>) and a circular outer rim (solid line in <figref idrefs="DRAWINGS">FIG. 5</figref>).

In a case where a tilt angle of the gantry <b>11</b> is “0°”, the inner rim and the outer rim (inner rim of the map T<b>1</b> of area outside imaging space) of the map T<b>2</b> of deteriorating area are formed as circles as shown in <figref idrefs="DRAWINGS">FIG. 5</figref>. In a case where the tilt angle of the gantry <b>11</b> is the value other than “0°”, they become oval. <figref idrefs="DRAWINGS">FIG. 5</figref> shows the maps at the rotary axis of the rotary unit <b>15</b> that coincides with the reconstruction center. However, it is not limited to the one shown in the drawing. The rotary axis of the rotary unit <b>15</b> does not have to coincide with the reconstruction center. In such the case, the inner rim and the outer rim of the map T<b>2</b> of deteriorating area may have an area that a part of is chipped off.

Furthermore, on the planar slice S<b>1</b> (shown in <figref idrefs="DRAWINGS">FIG. 4</figref>), the map T<b>2</b> of deteriorating area is not generated when the rotary axis of the rotary unit <b>15</b> (shown in <figref idrefs="DRAWINGS">FIG. 1</figref>) coincides with the reconstruction center.

The CT scan executing unit <b>56</b> (shown in <figref idrefs="DRAWINGS">FIG. 2</figref>) has a function to rotate the rotary unit <b>15</b> of the gantry <b>11</b> and to acquire the projection data by performing the CT scan. During the CT scan, the object M is positioned within the cavity of the rotary unit <b>15</b> for fixing the position in the z-axis direction, the X-ray beam from the X-ray tube <b>21</b> is irradiated to the object (X-ray projection), and a transmission X-ray is detected by the X-ray detector <b>24</b>. The detection of the transmission X-ray is performed in N view directions (N=1000, for example) while rotating the X-ray tube <b>21</b> and the X-ray detector <b>24</b> around the object M at “360°” (changing the projection angle). The detected transmission X-ray is converted into the digital value by the data acquisition system <b>25</b>, and transferred to the operation console <b>13</b> as the projection data via the IF <b>32</b><i>b</i>. The aforementioned series of the process may be referred to as a unit of “1” scan.

The storage of projection data controlling unit <b>57</b> has a function to control storage of the projection data transferred from the gantry <b>11</b> to the storage device, for example, the HD <b>44</b>.

The image processing unit <b>58</b> has a function to reconstruct the CT image, to implement an image processing for the CT image such that the deteriorating area is discriminated from the non-deteriorating area, and to make the display device <b>47</b> display the processed image. The image processing unit <b>58</b> changes a feature of the image processing so as to be discriminable between the deteriorating area and the non-deteriorating area by performing the image processing for changing at least one of a gray-scale conversion feature and a tone feature on the CT image. The image processing unit <b>58</b> may perform the image processing to delete data corresponding to the deteriorating area from data of the CT image such that the deteriorating area is discriminated from the non-deteriorating area. Alternatively, the image processing unit <b>58</b> may perform at least any one of operations to hide the display, to change a color, and to lower a contrast with respect to the deteriorating area on the CT image such that the deteriorating area is discriminated from the non-deteriorating area. The image processing unit <b>58</b> may further be structured to display a boundary line to a circular inner rim of the deteriorating area (boundary between the deteriorating area and the non-deteriorating area) such that the deteriorating area is discriminated from the non-deteriorating area. More specifically, the image processing unit <b>58</b> has an image reconstruction processing unit <b>66</b> and a display controlling unit <b>67</b>.

The image reconstruction processing unit <b>66</b> has a function to generate the CT image (reconstruction image) by back projecting the inside of the “Calib_FOV” (the deteriorating area and the non-deteriorating area) on each at the planar slice based on the projection data acquired by the CT scan executing unit <b>56</b> and stored in the storage of projection data controlling unit <b>57</b>, or the projection data preliminarily stored in the storage device such as the HD <b>44</b>. The image reconstruction process used for a conventional scan, a dynamic scan and a real time scan is performed using the algorithm that allows faithful reproduction of the cone angle in the z-axis direction.

The display controlling unit <b>67</b> has a function to control displaying of the image on the display device <b>47</b>. Specifically, the display controlling unit <b>67</b> has a map of area outside imaging space processing unit <b>68</b> and a map of deteriorating area processing unit <b>69</b>

The map of area outside imaging space processing unit <b>68</b> has a function to superimpose the map of area outside imaging space generated by the map of area outside imaging space generating unit <b>62</b> with the CT image reconstructed by the image reconstruction processing unit <b>66</b> in reference to the reconstruction center so as to convert a pixel value corresponding to the pixel within the map of area outside imaging space into the mask value (for example “−2048”) that makes the image invisible.

The map of deteriorating area processing unit <b>69</b> has a function to convert a display format within the map of deteriorating area by superimposing the map of deteriorating area, generated by the map of deteriorating area generating unit <b>63</b>, with the reconstructed CT image, generated by the image reconstruction processing unit <b>66</b>, in reference to the reconstruction center. The map of deteriorating area processing unit <b>69</b> is provided with at least one of a mask value replacing unit <b>69</b><i>a</i>, a variable mask value adding unit <b>69</b><i>b </i>and an edging-line setting unit <b>69</b><i>c. </i>

The mask value replacing unit <b>69</b><i>a </i>replaces the pixel value corresponding to the pixel within the map of deteriorating area with the mask value that makes the image invisible.

The variable mask value adding unit <b>69</b><i>b </i>adds the variable mask value to the pixel value corresponding to the pixel within the map of deteriorating area for making a transparency of the mask within the map of deteriorating area variable.

The edging-line setting unit <b>69</b><i>c </i>serves to provide the rim of the map of deteriorating area with an edging-line.

Furthermore, by a size of a pixel of a reconstruction matrix (including a volume), there is a case that there is a pixel equivalent to both with the deteriorating area and the non-deteriorating area, in a vicinity of a border with a pixel falling under the deteriorating area on the map of deteriorating area and a pixel falling under the non-deteriorating area not on the map of deteriorating area and not on the map of area outside imaging space. In this case, for the pixel equivalent to both, the processing as the deteriorating area or the non-deteriorating area may be performed. Or, for the pixel equivalent to both, a processing, like gradation processing, of unlike the processing of the deteriorating area and the non-deteriorating area may be performed.

<figref idrefs="DRAWINGS">FIGS. 6</figref>, <b>7</b> and <b>8</b> are each pattern diagram showing an example of display method of the image including the CT image.

Each display image in <figref idrefs="DRAWINGS">FIGS. 6</figref>, <b>7</b> and <b>8</b> shows the planar slice S<b>2</b> (shown in <figref idrefs="DRAWINGS">FIG. 4</figref>) representing the display image including the CT image in the case where the rotary axis of the rotary unit <b>15</b> coincides with the reconstruction center. <figref idrefs="DRAWINGS">FIG. 6</figref> is the display image obtained by allowing the mask value replacing unit <b>69</b><i>a </i>of the map of deteriorating area processing unit <b>69</b> to function to replace the pixel value of the pixel within the map T<b>2</b> of deteriorating area with the mask value. <figref idrefs="DRAWINGS">FIG. 7</figref> is the display image obtained by allowing the variable mask value adding unit <b>69</b><i>b </i>of the map of deteriorating area processing unit <b>69</b> to function to add the variable mask value to the pixel value corresponding to the pixel within the map T<b>2</b> of deteriorating area. The portion where the variable mask value is added to the pixel value is hatched. <figref idrefs="DRAWINGS">FIG. 8</figref> is the display image obtained by allowing the edging-line setting unit <b>69</b><i>c </i>of the map of deteriorating area processing unit <b>69</b> to function to provide the inner rim of the map T<b>2</b> of deteriorating area with the edging line (as solid circle in the drawing). In the case where the rotary axis of the rotary unit <b>15</b> does not coincide with the reconstruction center, the display image may have a missing portion.

In the present embodiment, the mask value replacing unit <b>69</b><i>a </i>of the map of deteriorating area processing unit <b>69</b> may be operated to discriminate the deteriorating area unsuitable for an inspection from the non-deteriorating area suitable for the inspection such that the pixel value within the map T<b>2</b> of deteriorating area is replaced with the mask value likewise the map T<b>1</b> of area outside imaging space, and the CT image that covers the non-deteriorating area is only displayed (see <figref idrefs="DRAWINGS">FIG. 6</figref>).

However, there may be a case where the replacement of the pixel values in the map T<b>2</b> of deteriorating area with the mask value makes it difficult to identify as to which portion (site) of the patient M<b>1</b> corresponds with the image within the deteriorating area, that is, difficult to determine the positional relationship to its entirety. In the present embodiment, the variable mask value adding unit <b>69</b><i>b </i>of the map of deteriorating area processing unit <b>69</b> is allowed to function to change the transparency of the mask applied to the map T<b>2</b> of deteriorating area such that the positional relationship of the image within the deteriorating area to the entirety is identified for displaying the CT image that covers both the non-deteriorating area and the deteriorating area (see <figref idrefs="DRAWINGS">FIG. 7</figref>). Accordingly, this may indicate that the image within the map T<b>2</b> of deteriorating area has the low quality, and the masked image within the map T<b>2</b> of deteriorating area is visible. The transparency of the mask applied to the map T<b>2</b> of deteriorating area may be set by the operator.

The edging-line setting unit <b>69</b><i>c </i>of the map of deteriorating area processing unit <b>69</b> is allowed to function to display the image (see <figref idrefs="DRAWINGS">FIG. 8</figref>) to obtain the same effect as the one derived from the variable mask value adding unit <b>69</b><i>b</i>. The edging-line may be arbitrarily selected by the operator from the solid line, the dashed line and the bold line (required to extend outward). The color of the edging-line may also be freely set by the operator.

The operation console <b>13</b> (shown in <figref idrefs="DRAWINGS">FIG. 2</figref>) may be operated as a scano-imaging executing unit <b>71</b> and a scanogram generating unit <b>72</b> for generating an image (scanogram) for a positioning of the patient M<b>1</b>.

In a case where the operation console <b>13</b> is operated as the scano-imaging executing unit <b>71</b> and the scanogram generating unit <b>72</b>, the map of area outside imaging space generating unit <b>62</b> has a function to generate the map of area outside imaging space of the area outside the diameter of the imaging space on the planar sagittal from the area outside the diameter of the imaging space on each planar slice at the rotary axis of the rotary unit <b>15</b> as the center based on the diameter of the imaging space (Calib_FOV) and the width of the X-ray detector <b>24</b> (DS) in the z-axis direction. In addition, the map of deteriorating area generating unit <b>63</b> has a function to generate the map of deteriorating area of the deteriorating area on the planar sagittal from the deteriorating area on each planar slice at the rotary axis of the rotary unit <b>15</b> as the center based on the diameter of the imaging space, the width of the X-ray detector <b>24</b> in the body axis direction, and the non-deteriorating area generated by the deteriorating area generating unit <b>61</b>.

<figref idrefs="DRAWINGS">FIG. 9</figref> is a diagram showing an example of the map of area outside imaging space and the map of deteriorating area.

<figref idrefs="DRAWINGS">FIG. 9</figref> shows the map T<b>1</b> of area outside imaging space generated from the outside imaging space area on each planar slice at the rotary axis of the rotary unit <b>15</b> (shown in <figref idrefs="DRAWINGS">FIG. 1</figref>) as the center to appear on the planar sagittal, and the map T<b>2</b> of deteriorating area generated from the deteriorating area to appear on the planar sagittal. In addition, <figref idrefs="DRAWINGS">FIG. 9</figref> shows the map T<b>1</b> of area outside imaging space and the map T<b>2</b> of deteriorating area to appear on the scanogram.

When the map T<b>1</b> of area outside imaging space and the map T<b>2</b> of deteriorating area are applied on the scanogram, the scanogram and an image of a mark indicating the scan range (dashed line in <figref idrefs="DRAWINGS">FIG. 9</figref>) may be displayed by superimposing. The map T<b>2</b> of deteriorating area may be displayed on the scanogram together with the scan range to clarify that the scan range is different from an imaging range (of the data with maintained quality). The image processing unit <b>67</b> may be structured to perform at least one of the image processing to hide the display, to change the color and to lower the contrast with respect to the deteriorating area on the scanogram.

The scano-imaging executing unit <b>71</b> has a function to execute a scano-imaging. In the scano-imaging, the X-ray irradiation and the data acquisition are performed while keeping the rotation of the rotary unit <b>15</b> stopped under the control of the main controller <b>31</b>. The projection data acquired through the scano-imaging are transmitted to the operation console <b>13</b>.

The scanogram generating unit <b>72</b> has a function to generate the scanogram by arranging the projection data transmitted to the operation console <b>13</b> in accordance with the detecting position via the storage device such as the HD <b>44</b> in the operation console <b>13</b>.

The operation console <b>13</b> may be operated as a planar reconstructing unit <b>81</b>.

In the case where the operation console <b>13</b> is allowed to function as the planar reconstructing unit <b>81</b>, the map of area outside imaging space generating unit <b>62</b> has a function to generate the map of area outside imaging space of the area outside the diameter of the imaging space appeared on the a planar-MPR (multi planar reconstruction), generated by using an MPR processing, from the area outside the diameter of the imaging space on each planar slice at the center that coincides with reconstruction center based on the diameter of the imaging space (Calib_FOV) and the width of the X-ray detector <b>24</b> (DS) in the z-axis direction. The map of deteriorating area generating unit <b>63</b> generates the map of deteriorating area of the deteriorating area appeared on the planar-MPR from the deteriorating area generated on each planar slice at the center that coincides with the reconstruction center based on the diameter of the imaging space, the width of the X-ray detector <b>24</b> in the body axis direction, and the non-deteriorating area generated by the non-deteriorating area generating unit <b>61</b>.

The planar reconstructing unit <b>81</b> has a function to generate an MPR image by reconstructing the image on the planar-MPR different from the CT image, that is, coronal image, sagittal image and oblique image, based on a plurality of CT images reconstructed by the image reconstruction processing unit <b>66</b>.

<figref idrefs="DRAWINGS">FIGS. 10 and 11</figref> are each diagram showing an example of display method of an image including the MPR (sagittal) image.

Each of <figref idrefs="DRAWINGS">FIGS. 10 and 11</figref> shows the MPR image obtained by scanning the cylinder M<b>2</b> that contains water and performing the planar reconstruction at the sagittal plane. <figref idrefs="DRAWINGS">FIG. 10</figref> shows the MPR image superimposed with the map T<b>2</b> of deteriorating area in which the pixel value is replaced with the mask value by the mask value replacing unit <b>69</b><i>a </i>of the map of deteriorating area processing unit <b>69</b>. Meanwhile, <figref idrefs="DRAWINGS">FIG. 11</figref> shows the MPR image in which the edging-line is drawn inside the inner rim of the map T<b>2</b> of deteriorating area by operating the edging-line setting unit <b>69</b><i>c </i>of the map of deteriorating area processing unit <b>69</b>. <figref idrefs="DRAWINGS">FIGS. 10 and 11</figref> show the display images in the case where the rotary axis of the rotary unit <b>15</b> coincides with the reconstruction center. However, it is not limited to the one as described above. The rotary axis of the rotary unit <b>15</b> does not have to coincide with the reconstruction center.

<figref idrefs="DRAWINGS">FIG. 12</figref> is a conceptual diagram showing an example of display method of the scanogram.

<figref idrefs="DRAWINGS">FIG. 12</figref> shows a concept of the scanogram in which the edging-line showing a scan area or an imaging area is drawn inside the inner rim of the map T<b>2</b> of deteriorating area by operating the edging-line setting unit <b>69</b><i>c </i>of the map of deteriorating area processing unit <b>69</b>. In addition, when the scanogram is displayed, it is chosen display of the deteriorating area or non-display of the deteriorating area.

The embodiment of the present invention may be applied to the processing of a three-dimensional image generated based on a plurality of CT images at the corresponding planar slices. The image processing unit <b>58</b> obtains a range of the deteriorating areas and the non-deteriorating areas on the CT images at the respective plural planar slices, and performs the image processing for the three-dimensional image obtained based on the CT images so as to discriminate the deteriorating area from the non-deteriorating area.

According to the X-ray CT apparatus <b>10</b> of the present embodiment, the image that can effectively perform an inspection and an interpretation of radiogram is offered by generating the image obtained by appropriately changing the display format on the non-deteriorating area.

<figref idrefs="DRAWINGS">FIG. 13</figref> is a block diagram showing an embodiment of the image display apparatus according to the present invention.

<figref idrefs="DRAWINGS">FIG. 13</figref> shows a generally employed X-ray CT apparatus <b>88</b> which acquires the projection data while rotating the X-ray source for emitting the X-ray beam and the X-ray detector with multi-arrayed detecting elements along the slice direction around the rotary axis to perform the back projection in consideration with the cone angle of the X-ray beam such that the CT image is reconstructed, and an image display apparatus (viewer) <b>89</b> connected to the X-ray CT apparatus <b>88</b> so as to be communicated via the network N.

The image display apparatus <b>89</b> is formed of a basic hardware including a CPU <b>91</b>, a memory <b>92</b>, a HD <b>94</b>, an IF <b>95</b>, an input device <b>96</b> and a display device <b>97</b>. The CPU <b>41</b> is interconnected with the respective units of the hardware for constituting the image display apparatus <b>89</b> via a bus B<b>2</b> as the common signal transmission path. A drive for medium <b>98</b> may be added to the image display apparatus <b>89</b>. In the embodiment, the image display apparatus <b>89</b> is structured to obtain the CT image from the X-ray CT apparatus <b>88</b> via the network N. However, it is not limited to the aforementioned structure. It may be structured to record the CT image generated by the X-ray CT apparatus <b>88</b> in the recording medium that will be read by the drive for medium <b>98</b> of the image display apparatus <b>89</b> for obtaining the CT image from the X-ray CT apparatus <b>88</b>.

As the CPU <b>91</b>, the memory <b>92</b>, the HD <b>94</b>, the IF <b>95</b>, the input device <b>96</b>, the display device <b>97</b> and the drive for medium <b>98</b> have the same functions as those of the respective units as shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, that is, the CPU <b>41</b>, the memory <b>42</b>, the HD <b>44</b>, the IF <b>45</b>, the input device <b>46</b>, the display device <b>47</b> and the drive for medium <b>48</b>, explanations of those components will be omitted.

<figref idrefs="DRAWINGS">FIG. 14</figref> is a functional block diagram showing the image display apparatus <b>89</b>.

Upon execution of the program by the CPU <b>91</b> of the image display apparatus <b>89</b> (shown in <figref idrefs="DRAWINGS">FIG. 13</figref>) the image display apparatus <b>89</b> functions as the area arithmetic unit <b>55</b> and the display controlling unit <b>67</b>. In the present embodiment, the respective units <b>55</b> and <b>67</b> are operated by execution of the program. However, the respective functions of those units may be formed as the hardware of the image display apparatus <b>89</b>.

As has been described referring to <figref idrefs="DRAWINGS">FIG. 2</figref>, the area arithmetic unit <b>55</b> has the non-deteriorating area generating unit <b>61</b>, the map of area outside imaging space generating unit <b>62</b>, and the map of deteriorating area generating unit <b>63</b>.

The display controlling unit <b>67</b> has the map of area outside imaging space processing unit <b>68</b> and the map of deteriorating area processing unit <b>69</b> as has been described referring to <figref idrefs="DRAWINGS">FIG. 2</figref>.

The display controlling processing unit <b>67</b> of the image display apparatus <b>89</b> displays the CT image on the display device <b>97</b> such that the deteriorating area is discriminated from the area other than the deteriorating area based on the information with respect to the position of the deteriorating area obtained by the area arithmetic unit <b>55</b>. The person who interprets the radiogram, for example, doctor is able to interpret while viewing the display image on the display device <b>97</b>. This makes it possible to the interpreter of the radiogram to perform accurate interpretation with the display image.

The image display apparatus <b>89</b> of the present embodiment generates the display image obtained by appropriately changing the display format of the non-deteriorating area with relatively sufficient projection data, based on which the inspection and interpretation of the radiogram are optimally performed.

According to the image display apparatus <b>89</b> of the present embodiment, the image that can effectively perform an inspection and an interpretation of radiogram is offered by generating the image obtained by appropriately changing the display format on the non-deteriorating area.